Some users make their PCs available to BOINC projects 24/7, others 8/5 etc. Also home users will tend to switch their PCs off when they go on holiday.

So my suggestion is for BOINC to include a calendar so users can enter when they anticipate having computer power available to BOINC, and for how many hours. The scheduler would use this to stop it asking for work-units which time out because of lack of PC availability.